Known in the art are methods for the determination of depth of water-seepage strata, comprising lifting the drill tool and lowering special flow meters (Driller's Handbook by V. I. Mischevich, vol. II, published 1973, "Nedra" Publishers, Moscow, p. 88 (in Russian)).
These methods are dificient in a low sensitivity of flow meters which cannot detect a stratum at low quantities of fluids entering the mud.
Known in the art is a method for the determination of depth of a water-seepage stratum, comprising a short-time suspension of drilling mud supply with subsequent restoration of circulation and detection at the surface of the batch of the drilling mud diluted with fluid from the change in density of the drilling mud compared to the original density, and measuring the time since the beginning of pumping till the appearance at the surface of the batch of drilling mud diluted with fluid (Bull. "Discoveries, Inventions Industrial Designs and Trademarks" USSR Inventor's Certificate No. 484301 Published in No. 34 of 1975, IPC E 21 b, 47 04).
This prior art method is also characterized by low accuracy with small differences in densities of the drilling mud and stratum fluid so that the application of this method is rather limited.